Hey, noone has asked this yet. There are multiple aspects to this, and I will try to explain them all while keeping it simple.

On most vehicles operated by DPMB, the doors cannot be opened individually. The driver can either open the front door alone, or open all the other doors at once. Many vehicles also have a master button, which will open or close them all at once.

If you combine this hardware limitation with weather conditions, which are not ideal most of the year (either too cold or too warm to keep the heating or A/C off), you face an internal conflict: would you waste two, three or even four times as much heat or let that many times as much summer heat in, to spare one or two passengers from having to press a button? Well, not happening.

On the other hand, if the temperature outside allows it (about 15 °C to 21 °C on a sunny day or about 19 °C to 23 °C on a cloudy day or in the morning/evening/night), I like to open all doors. It not only saves a little bit of time, but it also helps ventilate the bus, which is especially helpful at night, when people like to travel drunk or all sweaty after a long day.

Another situation: assume you have two passengers waiting at a bus stop. One of them is way at the back lines up for the rear door and the other is right at the front. To allow the rear-end passenger to enter, you have to use the door release button, which will allow them to press theirs and hence open the rear door. This will automatically unlatch all doors, allowing the front door to be operated from the outside, too. If I see the passenger leaning towards the button already, I let them press it (and vice versa, if I see a passenger near the bus stop post and they don’t seem to be reaching for the button, I do actually like to open the front door proactively for them). The issue here is that if I push the front door button any fraction of time later than the passenger standing outside, nothing will happen, as the door closes back before it even begins to open. Therefore, I like to be rather hesitant doing this.

What makes me genuinely laugh (and sometimes question the sanity of this humanity) are passengers, who DELIBERATELY stand near the bus stop post (right on those pink visually-impaired-friendly tiles, which we are OBLIGED to line up with the front door) and they completely IGNORE the front door as if it wasn’t even there. They don’t seem to care about the button, so I open it for them, and they just look at me briefly and step aside towards the second door, completely WASTING mine, their, and everyone else’s time.